Substrates for growing group iii nitride crystals and their fabrication method

Abstract

In one instance, the invention provides a substrate for growing a thick layer of group III nitride. The substrate has a first surface prepared for epitaxial growth of group III nitride and a second surface, opposite to the first surface, having a plurality of grooves. The invention also provides a method of producing a thick layer or a bulk crystal of group III nitride using a grooved substrate. The grooved substrate in one configuration grows a thick layer or a bulk crystal of group III nitride with reduced bow and/or spontaneous separation from the substrate.

What is claimed is: 
     
         1 . A substrate for growing a group III nitride layer, and wherein the substrate has
 (a) a first side suitable for epitaxial growth of bulk group III nitride, and   (b) a second side opposite to the first side of the substrate and having a plurality of grooves.   
     
     
         2 . A substrate according to  claim 1  wherein width of said grooves is individually between 100 microns and 300 microns and depth of said grooves is individually between 50 microns and 75% of a thickness of the substrate. 
     
     
         3 . A substrate according to  claim 1  wherein pitch of the grooves is individually between 0.1 mm and 5 mm. 
     
     
         4 . A substrate according to  claim 1  wherein the grooves are along crystallographic orientations of the substrate. 
     
     
         5 . A substrate according to  claim 4  wherein the crystallographic orientation is a cleavage direction of the substrate. 
     
     
         6 . A substrate according to  claim 1  wherein the plurality of grooves have a size, shape, and placement on said second side such that the substrate provides less bowing in a group III nitride layer formed on said substrate than a comparative substrate that is otherwise identical but does not have said grooves on the second side of the comparative substrate. 
     
     
         7 . A substrate according to  claim 1  wherein the grooves have a size, shape, and placement on said second side such that the substrate provides a greater rate of growth of a group III nitride layer on said substrate than a comparative substrate that is otherwise identical but does not have said grooves on the second side of the comparative substrate. 
     
     
         8 . A substrate according to  claim 1  wherein the grooves have a size, shape, and placement on said second side such that the substrate fully or partially separates from a group III nitride layer grown on the first side of the substrate when the group III nitride layer has a thickness of more than 500 microns. 
     
     
         9 . A substrate according to  claim 1  wherein the grooves are spaced more closely in a central area of the second side than toward an edge of the second side. 
     
     
         10 . A substrate according to  claim 1  wherein the substrate is single crystalline sapphire. 
     
     
         11 . A substrate according to  claim 10  wherein the first side and the second side are c-planes of said single crystalline sapphire having miscut within 5 degree. 
     
     
         12 . A substrate according to  claim 11  wherein the grooves have three-fold symmetry along m-planes of the single crystalline sapphire. 
     
     
         13 . A substrate according to  claim 1  wherein the grooves are formed using a multiple wire saw. 
     
     
         14 . A substrate according to  claim 13  wherein the surface of the grooves have mechanical scratches along the groove direction. 
     
     
         15 . A substrate according to  claim 1  wherein the first side has no grooves. 
     
     
         16 . A substrate according to  claim 1  wherein the substrate has a buffer layer on the first side of the substrate. 
     
     
         17 . A substrate according to  claim 1  wherein the group III nitride is GaN. 
     
     
         18 . A substrate according to  claim 17  wherein the grooves are along crystallographic orientations of the substrate. 
     
     
         19 . A substrate according to  claim 18  wherein the crystallographic orientation is a cleavage direction of the substrate. 
     
     
         20 . A substrate according to  claim 19  wherein the first side and the second side are c-planes of said single crystalline sapphire having miscut within 5 degree and wherein the grooves have three-fold symmetry along m-planes of the substrate.